This invention relates to a hydrophobic coating to be used in the context of coated articles. More particularly, this invention relates to a hydrophobic coating comprising a layer having a contact angle(s) xcex8 which does not significantly decrease upon exposure to ultraviolet (UV) radiation. In certain example embodiments, the layer may be of or include NiCrOx, or any other suitable material.
Hydrophobic coatings are known in the art, and are typically characterized by high contact angles xcex8. Contact angles, in general, are discussed for example in U.S. Ser. Nos. 09/442,805 filed Nov. 18, 1999 (now U.S. Pat. No. 6,338,901), and 09/583,862 filed Jun. 1, 2000 (now U.S. Pat. No. 6,335,086), both of which are hereby incorporated herein by reference. Contact angle xcex8 is explained in the context of FIGS. 1 and 2.
The initial contact angle xcex8 of a conventional glass substrate 1 with sessile water drop 3 thereon is typically from about 22-24 degrees, although it may dip as low as 17 or so degrees in some circumstances, as illustrated in FIG. 1. Thus, conventional glass substrates are not particularly hydrophobic in nature. The provision of a hydrophobic coating or layer system 5 on substrate 1 causes the contact angle xcex8 to increase to the angles discussed herein, as shown in FIG. 2. As shown in FIG. 2, hydrophobic coatings can have initial contact angles xcex8 of above 90 degrees for water repelling purposes. An xe2x80x9cinitialxe2x80x9d contact angle xcex8 means prior to exposure to environmental conditions such as sun, rain, abrasions, ultraviolet radiation, humidity, etc.
For example, U.S. Pat. No. 5,378,527 discloses a diamond-like carbon (DLC) coating having a contact angle of 90 degrees in certain examples, and 120 degrees in other examples. Unfortunately, it has been found that initial contact angles xcex8 of DLC coatings drop dramatically upon prolonged exposure to ultraviolet (UV) radiation in an ambient atmosphere including sun, rain and the like. This UV stability problem can in some instances result in contact angle xcex8 dropping from an initial value of 80 degrees or higher to a post-UV value of less than 20 degrees.
In view of the above, those skilled in the art will appreciate that there exists a need in the art for a UV stable hydrophobic coating which does not experience a significant loss/decrease in contact angle xcex8 value upon prolonged exposure (e.g., 100-250 hours) to UV radiation. Other needs will also become apparent to those skilled in the art upon review of the instant document.
An object of this invention is to provide a hydrophobic coating that has a rather high contact angle xcex8 of at least about 70 degrees, both before and after exposure to ultraviolet (UV) radiation (e.g., about 100-250 hours of UV exposure). In other words, an object of this invention is to provide a hydrophobic coating that is UV stable (i.e., not subject to significant contact angle xcex8 degradation upon UV exposure).
Another object of this invention is to provide hydrophobic coating that is transmissive of at least 60% of visible light, more preferably at least 70% of visible light, and most preferably at least 75% of visible light.
Another object of this invention is to provide a hydrophobic coating that is durable enough to be used in the context of vehicle windows, architectural windows, and/or the like.
Another object of this invention is to provide a hydrophobic coating including at least one NiCrOx inclusive layer.
Another object of this invention is to fulfill one or more of the above listed objects and/or needs.